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Undifferentiated spondyloarthropathy:[18, 31]

Undifferentiated spondyloarthropathy is a syndrome with features consistent with the spondyloarthropathies, but affected patients do not fulfill criteria for any specific spondyloarthropathy. Criteria are outlined in Table 2 at the end of this section.

Undifferentiated spondyloarthropathy may represent an early phase or incomplete form of ankylosing spondylitis or another spondyloarthropathy. In fact, several studies of undifferentiated spondyloarthropathy included many patients who probably should have been diagnosed with ankylosing spondylitis, reactive arthritis, or IBD-associated spondyloarthropathy, which made the clinical description very ambiguous. However, more recent data suggest that these patients may represent a distinct disease entity based on demographic and clinical criteria.

Although no specific criteria are identified, using modified Amor criteria can be helpful in confirming a clinical diagnosis.[19]

Distinguishing features of undifferentiated spondyloarthropathy:[19]

The age of onset has a very wide range, with the peak onset at approximately age 50 years. The male-to-female ratio is 1:3. The onset is usually insidious, and, even after years of active disease, sacroiliitis and spondylitis are either absent or appear very mild on routine radiography.

Clinical manifestations of undifferentiated spondyloarthropathy include inflammatory back pain (90%), buttock pain (80%), enthesitis (85%), peripheral arthritis (35%), dactylitis (17%), and fatigue (55%).

Extra-articular manifestations are uncommon, occurring in fewer than 10% of patients, and include acute anterior uveitis (1-2%), oral ulcers, rash, nonspecific IBD, pleuritis, and pericarditis.

Findings of laboratory studies are generally unremarkable except for the presence of an elevated ESR or C-reactive protein level (36%). HLA-B27 antigen is positive only in approximately 20-25% of patients.

These factors, especially the late age of onset, female predominance, and low HLA-B27 positivity, suggest that Undifferentiated spondyloarthropathy is distinct from ankylosing spondylitis and the other classic spondyloarthropathies.

In addition, when these patients are observed over long periods, they rarely develop clinical manifestations or radiographic changes that result in a change of diagnosis (outlined in Table 3, at the end of this section). Occasionally, radiographs show evidence of periosteal new bone formation at sites of enthesitis, especially at the insertion of the Achilles tendon or plantar fascia on the calcaneus, or early syndesmophytes on the lumbar spine without bridging.

Although most patients with undifferentiated spondyloarthropathy have chronic, active disease and require long-term therapy, some patients have mild and intermittent symptoms that require intermittent symptomatic therapy. These episodes may last from 1-2 weeks to several months, with long asymptomatic periods that do not require therapy.

Most patients with undifferentiated spondyloarthropathy (>75%) require long-term therapy for ongoing symptomatic disease. Most patients respond well to nonsteroidal anti-inflammatory drugs (NSAIDs). Most patients maintain good function without progressive disease or clinically significant radiographic changes. A small minority of patients does not respond well to or tolerate NSAIDs. In these patients, treatment progression is similar to patients with ankylosing spondylitis, including the use of sulfasalazine, methotrexate, and TNF-α antagonists, although no well-designed clinical trials have been conducted on the treatment of undifferentiated spondyloarthropathy.

Table 2. Diagnostic Criteria for Undifferentiated Spondyloarthropathy Using Modified Amor Criteria[32, 33] (Open Table in a new window)

Inclusion Criteria Exclusion Criteria
Inflammatory back pain 1 point Diagnosis of specific spondyloarthropathy
Unilateral buttock pain 1 point Sacroiliitis on radiograph ≥ grade 2
Alternating buttock pain 2 points Precipitating genitourinary/GI infection
Enthesitis 2 points Psoriasis
Peripheral arthritis 2 points Keratoderma blennorrhagicum
Dactylitis (sausage digit) 2 points IBD (Crohn disease or ulcerative colitis)
Acute anterior uveitis 2 points Positive rheumatoid factor
HLA-B27 –positive or family history of spondyloarthropathy 2 points Positive antinuclear antibody, titer >1:80
Good response to nonsteroidal anti-inflammatory drugs 2 points
Diagnosis of spondyloarthropathy with 6 or more points
Table 3. Clinical and Laboratory Features of Undifferentiated Spondyloarthropathy (Open Table in a new window)

Clinical Feature of Undifferentiated Spondyloarthropathy Frequency
Inflammatory back pain 90%
Buttock pain 80%
Enthesitis 75%
Peripheral arthritis 40%
Dactylitis (sausage digits) 20%
Acute anterior uveitis 1-2%
Fatigue 55%
Elevated ESR 32%
HLA-B27 –positive 25%